Wavelockers, devices used to maintain laser wavelengths, are extensively used in transmitters of telecommunication systems and can also be used to stabilize lasers used to pump amplifiers in such systems. Additionally, present day telecommunication amplifiers are requiring increasing levels of wavelength stable pump power that can be realized by multiplexing stabilized lasers of more than one wavelength and/or polarization.
U.S. Pat. No. 6,351,583 B1 (Bergmann et al.), issued on Feb. 26, 2002, discloses an optical apparatus for multiplexing a plurality of optical signals of different wavelengths by a frequency routing device to provide a multiplexed output signal. The frequency routing device comprises a plurality of input waveguides, each waveguide being coupled at its input end to a corresponding one of a plurality of lasers, and at the other end to an arrangement including a first star coupler, and a second star coupler interconnected by way of an array waveguide comprising a plurality of optical fibers of unequal length. An optical waveguide is connected to a first output port of the second star coupler for providing a multiplexed output optical signal from each of the plurality of lasers. First and second cross-coupling output ports from the second star coupler, located on opposite sides of the first output port, provide first and second cross-coupling output signals. Each of the first and second cross-coupling output signals is representative of the cross-coupling of each of the multiplexed optical signals with the cross-coupling output signals. The first and second cross-coupling output signals are equally strong for any given optical signal forming the multiplexed output signal when the optical signal has a wavelength substantially equal to a specified wavelength for that given optical signal. The first and second cross-coupling output signals are each converted to a separate electrical signal that are subtracted from one another in a subtracter. If there is no difference detected between the cross-coupling output signals for an optical signal, then a zero value will be generated at the output of the subtracter. If a difference in the cross-coupling output signals is detected by the subtraction process for any one of the multiplexed optical signals, the subtracter generates a control signal for that wavelength that is further processed and used to stabilize the associated laser generating that optical wavelength signal. One problem with this arrangement is that the stabilization feedback is performed on multiplexed signals and is dependent on having signal modulation for the detection of which wavelength in the multiplexed signal is drifting.
It is desirable to provide a grating based wavelength multiplexer and wavelength stabilizer that is not performed on multiplexed signals but rather on resolved separate wavelength signals generated by each of at least two radiation sources.